The assessment of body composition, including measurement of fat and fat-free mass, provides physicians with important information regarding physical status. Excess body fat has been associated with a variety of disease processes, such as cardiovascular disease, is diabetes, hypertension, hyperlipidemia, kidney disease, and musculoskeletal disorders. Low levels of fat free mass have been found to be critically adverse to the health of certain at-risk populations, such as the elderly, infants, and those suffering from muscle wasting diseases.
Assessment of body composition has also been found to be useful in the context of evaluating and improving athletic performance. Generally, athletes require a high strength to weight ratio to achieve optimal athletic performance. Because body fat adds weight without a commensurate increase in strength, low body fat percentages have been emphasized within many athletic fields. However, too little body fat can result in deterioration of both health and athletic performance. Thus, accurate measurement of body composition has been found extremely useful in analysis of athletic performance.
A variety of methods are currently used in the assessment of body composition. One common method is a skinfold measurement, typically performed using calipers that compress the skin at certain points on the body. While non-invasive, this method suffers from poor accuracy on account of variations in fat patterning, misapplication of population specific prediction equations, improper site identification for compressing the skin, poor fold grasping, and the necessity for significant technician training to administer the test properly.
Another method employed is bioelectric impedance analysis (“BIA”). Bioelectric impedance measurements rely on the fact that the body contains intracellular and extracellular fluids that are capable of conducting electricity. By passing a high frequency electric current through the body, BIA determines body composition based on the bodies, measured impedance in passing current, and the known impedance values for human tissue. However, the accuracy of this method is greatly affected by the state of hydration of the subject, and variations in temperature of both the subject and the surrounding environment.
The most common method currently used when precision body mass measurements are required is hydrostatic weighing. This method is based upon the application of Archimedes principle, and requires weighing of the subject on land, repeated weighing of the subject under water, and an estimation of air present in the lungs of the subject using gas dilution techniques. However, hydrodensitometry is time consuming, typically unpleasant for the subjects, requires significant subject participation such as repeated, complete exhalation of air from the subject's lungs, requires considerable technician training and, due to the necessary facilities for implementation, is unsuitable for clinical practice. Further, its application to populations who would particularly benefit from body-mass measurement, such as the obese, elderly, infants, or cardiac patents, is precluded by the above concerns.
One technique offering particular promise in performing body mass measurement is the use of plethysmography. Plethysmographic methods determine body composition through application of Boyle's law to the differentiation in volume between the volume of an empty measurement chamber, and the volume of the chamber with the subject to be measured inside. Examples of this technique are disclosed in U.S. Pat. No. 4,369,652 issued to Gundlach, U.S. Pat. No. 5,450,750 issued to Abler, U.S. Pat. No. 4,184,371 issued to Brachet, and U.S. Pat. No. 5,105,825 issued to Dempster. This procedure, in contrast to hydrodensitometry, generally does not cause anxiety or discomfort in the subject, and due to the ease and non-invasiveness of the technique, can readily be applied to populations for whom hydrodensitometry is impractical.
However, to the present, plethysmographic methods have demonstrated problems with accuracy. For example, failure to take into account differences in compressibility of air in the chamber as opposed to air in the lungs of the subject can result in significant variability in measurements. Although some effort has been made to address these considerations, as disclosed by Dempster, U.S. Pat. No. 5,105,825, the greatest practical impediment to widespread application of plethysmography is the necessity for repeatable, precise volume within the measurement chamber.
As noted by Gundlach, et al., “The Plethysmometric Measurement of Total Body Volume,” Human Biology, Vol. 38, No. 5, p.783-99, large variations in measured body composition occur based on small changes of volume in the measurement chamber, due to nonrepeatability in the closing action employed for measurement chambers. Variability in closure pressure, and various stresses and strains in both the chamber door and chamber wall for plethysmographic chambers likewise contribute to the inaccuracy of body composition measurements. While current plethysmographic systems have to a certain degree been able to provide mechanical stability with respect to the method of ingress and egress necessary to generate accurate measurements, such systems are typically very complex, expensive, and labor-intensive to manufacture.
In view of the foregoing drawbacks, it would be desirable to provide apparatus and methods for accurate, non-invasive determination of body mass.
It would further be desirable to provide apparatus and methods for providing repeatable door closure in a plethysmographic chamber to ensure accurate, precise volume measurements.
It would further be desirable to provide robust, inexpensive, and easy to manufacture systems for providing repeatable door closure in a plethysmographic chamber.